DESCRIPTION

timer_settime() arms or disarms the timer identified by timerid. The
new_value argument is an itimerspec structure that specifies the new
initial value and the new interval for the timer. The itimerspec
structure is defined as follows:
struct timespec {
time_t tv_sec; /* Seconds */
long tv_nsec; /* Nanoseconds */
};
struct itimerspec {
struct timespec it_interval; /* Timer interval */
struct timespec it_value; /* Initial expiration */
};
Each of the substructures of the itimerspec structure is a timespec
structure that allows a time value to be specified in seconds and
nanoseconds. These time values are measured according to the clock
that was specified when the timer was created by timer_create()
If new_value->it_value specifies a nonzero value (i.e., either subfield
is nonzero), then timer_settime() arms (starts) the timer, setting it
to initially expire at the given time. (If the timer was already
armed, then the previous settings are overwritten.) If
new_value->it_value specifies a zero value (i.e., both subfields are
zero), then the timer is disarmed.
The new_value->it_interval field specifies the period of the timer, in
seconds and nanoseconds. If this field is nonzero, then each time that
an armed timer expires, the timer is reloaded from the value specified
in new_value->it_interval. If new_value->it_interval specifies a zero
value then the timer expires just once, at the time specified by
it_value.
By default, the initial expiration time specified in
new_value->it_value is interpreted relative to the current time on the
timer’s clock at the time of the call. This can be modified by
specifying TIMER_ABSTIME in flags, in which case new_value->it_value is
interpreted as an absolute value as measured on the timer’s clock; that
is, the timer will expire when the clock value reaches the value
specified by new_value->it_value. If the specified absolute time has
already passed, then the timer expires immediately, and the overrun
count (see timer_getoverrun(2)) will be set correctly.
If the value of the CLOCK_REALTIME clock is adjusted while an absolute
timer based on that clock is armed, then the expiration of the timer
will be appropriately adjusted. Adjustments to the CLOCK_REALTIME
clock have no effect on relative timers based on that clock.
If old_value is not NULL, then it returns the previous interval of the
timer (in old_value->it_interval) and the amount of time until the
timer would previously have next expired (in old_value->it_value).
timer_gettime() returns the time until next expiration, and the
interval, for the timer specified by timerid, in the buffer pointed to
by curr_value. The time remaining until the next timer expiration is
returned in curr_value->it_value; this is always a relative value,
regardless of whether the TIMER_ABSTIME flag was used when arming the
timer. If the value returned in curr_value->it_value is zero, then the
timer is currently disarmed. The timer interval is returned in
curr_value->it_interval. If the value returned in
curr_value->it_interval is zero, then this is a "one-shot" timer.

RETURNVALUE

On success, timer_settime() and timer_gettime() return 0. On error, -1
is returned, and errno is set to indicate the error.

ERRORS

These functions may fail with the following errors:
EFAULTnew_value, old_value, or curr_value is not a valid pointer.
EINVALtimerid is invalid.
timer_settime() may fail with the following errors:
EINVALnew_value.it_value is negative; or new_value.it_value.tv_nsec is
negative or greater than 999,999,999.